IDENTIFICATION AND COMPARISON OF MOVEMENT STRATEGIES OF THE SPIKE JUMP IN DIFFERENT PERFORMANCE LEVELS IN FEMALE VOLLEYBALL

INTRODUCTION: The spike jump is one of the most frequently perf ormed actions by attacking volleyball players. Higher jumps lift the point of attack, enabling the player to attack in steeper angles and of fering him more opportunities as he is less affected by the op ponents block. The technical execution of the complex and asymmetric move ment appears to have a major impact on jump height and therefore the success of action. The aim of this study was to examine and compare the kinetics and muscle activation patterns of the spike jump in different performance levels. METHODS: 27 female players from 2nd (Div2) and 8th (Div8) divisi on were investigated using a 3D movement analysis setup. Subjects performed 10 spike jumps with a 3 step approach, attacking a su spended stationary volleyball on their individually preferred height. Ground reaction forces (GRF) for each leg were recorded by two force plates. Muscle activation of knee and ankle extensors and flexors were measured bilaterally via EMG surface electrodes. For data analysis GRF (peak, integrals and timeseries) and EMG (integrals, timeseries) were calculated during ground contact. Discrete parameters were compared using Matlabs Wilcoxon’s tests while timeseries were compared using t-tests of statistical parametric mapping (SPM). The alpha level was set to 0.05 for all tests. RESULTS: Div8 generated a significantly higher vertical peak GRF (pGRFz) in the second step (step2) (p=.027) compared to the third step (step3), whereas Div2 revealed no significant side difference. Comparing both groups, Div2 generated a higher impulse of step3 (p<.001) and of both steps together (p=.035). SPM displayed a significantly higher GRFz for step3 in the second half of ground contact for Div2 (p=.010), as well as higher breaking forces for step3 in Div8 (p=.010). Moreover, significantly higher EMG integrals of the m. Soleus (step3) (p=.049) and m. Vastus Lateralis (step3) (p=.012) were found for Div2. First results also show higher knee flexion angles in Div2. CONCLUSION: Div2 players are able to generate a higher vertical GRF impulse in step3 and in step 2 and 3 together by generating higher GRFz during the second half of stance of step3. This is important as the generation of GRFz is known to be the performance-limiting factor of jump height. The generation of pGRFz is also more balanced in Div2 players which supports a two legged jump, while Div8 players showed significant differences between step2 and step3. Moreover, Div2 showed higher activations of ankle- and knee extensors in step 3. Increased knee flexion angles and the position of the Center of Mass more centrally over the feet are therefore advantageous to Div2 for generating greater GRFz, whereas Div8 experienced a higher breaking force which counteracts the generation of GRFz.